Immunoglobulin E(IgE) is one of an immunoglobulin group, which plays a role in allergic reactions. The IgE, which is secreted from B cells or is expressed on the surface of the B cells, binds to a high affinity IgE receptor (FcεRI) found on the surface of mast cells, basophils, etc. When an antigenic protein binds to IgE on a mast cell surface receptor, the IgE becomes a form in which it crosslinks the antigen. Thereafter, chemical mediators such as histamine or serotonin, which are stored in intracellular granules, are released. Consequently, an inflammatory reaction is induced, and type I allergy symptoms such as telangiectasis or vascular hyperpermeability are provoked (Non Patent Literature 1).
Accordingly, since a compound or a protein, which inhibits the binding of IgE to FcεRI, inhibits the binding of the IgE to the FcεRI found on the surface of mast cells, basophils, etc., such a compound or a protein is expected as a therapeutic agent for type I allergic diseases such as bronchial asthma, allergic rhinitis, and allergic conjunctivitis (Non Patent Literature 2).
In recent years, not only a conventional pharmaceutical product comprising, as an active ingredient, a low-molecular-weight compound, but also a protein pharmaceutical product, which strongly binds to a specific receptor or the like in a living body and exhibits excellent therapeutic effects, has been developed. For example, Etanercept has been known as a therapeutic agent for rheumatoid arthritis. Such Etanercept is a completely humanized soluble TNFα/LTα receptor formulation, which has been focused because of the role of a soluble receptor of a tumor necrosis factor (TNF) to suppress the action of TNF in a living body, and has been then developed.
The protein pharmaceutical product can be expected to have high therapeutic effects. On the other hand, it may cause a problem specific to the protein pharmaceutical product in the production process thereof.
In general, when an antibody or an Fc fusion protein is produced in the form of a pharmaceutical product, a purification method of using protein A is applied. In this method, a buffer with a low pH value is used to elute a protein of interest that binds to the protein A. Moreover, in order to inactivate virus, the protein of interest is desirably treated at low pH for a certain period of time.
A protein, which is poor in stability at low pH, easily forms aggregates. If the ratio of aggregates is high, a reduction in purification efficiency or production amount occurs in the production of protein pharmaceutical products. In addition, an immune response is provoked by mixing aggregates into pharmaceutical products, and as a result, serious side effects, such as anaphylaxis, are likely to occur.
As such, the instability of a protein of interest at low pH may be problematic in the production of protein pharmaceutical products.
A polypeptide (immunoadheson) comprising an immunoglobulin and an extracellular domain is disclosed in Patent Literature 1. Patent Literature 1 discloses a high affinity IgE receptor as an example of such immunoadheson. However, this publication does not specifically describe a fused protein of a high affinity IgE receptor and an immunoglobulin.
A fused protein (hereinafter referred to as “Fusion protein A”) of a high affinity IgE receptor α-chain (FcεRI α-chain; hereinafter referred to as “FCER1A”) and immunoglobulin G1 (IgG1) is disclosed in Non Patent Literature 3. However, the Fusion protein A disclosed in the aforementioned publication is largely different from the protein of the invention of the present application, in terms of the mode of binding FCER1A to IgG1 (Fc). That is to say, the protein of the invention of the present application has a characteristic amino acid sequence in a linker fragment region between the FcεRI and the IgG1.
A fused protein (NPB301) formed by linking a water-soluble fragment of the high affinity IgE receptor (FcεRI) to a human Fc region via a peptide linker is disclosed in Patent Literature 2. However, the protein of the invention of the present application does not comprise the peptide linker disclosed in Patent Literature 2. Moreover, Patent Literature 2 neither discloses nor suggests the characteristic amino acid sequence of the linker fragment region of the present invention.
A fused protein of FCER1A and immunoglobulin G2 (IgG2) is disclosed in Patent Literature 3. However, this fused protein comprising IgG2 is different from the protein of the invention of the present application, in terms of the amino acid sequences of a linker fragment region and an Fc region.
A fused protein of non-human primate FCER1A and IgG1 is disclosed in Patent Literature 4. Moreover, a fused protein of FCER1A and IgG1 is disclosed in Patent Literatures 5 to 7. However, these publications neither disclose nor suggest the characteristic amino acid sequence of the linker fragment region of the present invention.
The aforementioned Non Patent Literature 3 and Patent Literatures 1 to 7 neither disclose nor suggest the protein of the present invention.